84 ENERGY
regarded as basis of convenience which it would be well to retain, the fact constantly to be kept in mind is that the energetic condition never passes to either of them, and never can. This general characteristic holds true, whether expressed in terms of intensity or extensity of energy, whether of space, motion, force, degree of massive solidarity on the one hand, or of fineness of comminution of mass on the other. Any of these factors may pass to either very great or very small values, but none of them may ever attain to either zero or infinity.
Indeed, it will appear, as the argument proceeds, that every energetic relationship which can be stated exactly follows this same general law. To those engaged in power-engineering the most familiar illustration of this statement is the hyperbolic relation between the pressure and volume of any gas. Pressure and volume always appear as a product, each being inversely proportional to the other, or to some power of the other. The general equation is PVx=a constant. They never appear as a sum, one decreasing as the other increases. No degree of pressure, however great, can ever reduce the volume of any gas to zero; nor can any degree of expansion, however great, ever reduce the pressure to zero. There is no place in the universe where the pressure or density or volume of elastic matter is imaginably zero.
In every case, all energetic functions are founded upon a central, or mean energetic, condition, which hangs unsupported in space, so to speak, as the sun hangs in the heavens. No absolute base or support for it is imaginable or necessary. It is on either side of this central point of reference, and not up and down from any absolute zero, that all energetic factors vary. These statements, which have been made in reference to mechanical energy only, will be found to apply universally.
Energetic Equilibrium. In all natural phenomena the one most important guiding principle, after conservation, is that of universal stability of equilibrium. The determination of what shall be the next in that most intricate series of occurrences to which we give the general name, the progress of events, always depends upon stability of equilibrium. The natural universe is always, except locally and temporarily, in stable equilibrium. And if its equilibrium temporarily and locally has become unstable, the movement is always toward the recovery of stability.